{"id":"CVE-2026-33490","state":"PUBLISHED","title":"h3: Missing Path Segment Boundary Check in `mount()` Causes Middleware Execution on Unrelated Prefix-Matching Routes","description":"H3 is a minimal H(TTP) framework. In versions 2.0.0-0 through 2.0.1-rc.16, the `mount()` method in h3 uses a simple `startsWith()` check to determine whether incoming requests fall under a mounted sub-application's path prefix. Because this check does not verify a path segment boundary (i.e., that the next character after the base is `/` or end-of-string), middleware registered on a mount like `/admin` will also execute for unrelated routes such as `/admin-public`, `/administrator`, or `/adminstuff`. This allows an attacker to trigger context-setting middleware on paths it was never intended to cover, potentially polluting request context with unintended privilege flags. Version 2.0.2-rc.17 contains a patch.","publishedAt":"2026-03-26T17:19:15.956Z","updatedAt":"2026-03-26T18:23:39.653Z","severity":{"score":3.7,"label":"Low","version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N","source":"GitHub_M"},"assigner":"GitHub_M","products":["h3js h3"],"affected":[{"vendor":"h3js","product":"h3","versions":[{"version":">= 2.0.1-alpha.0, < 2.0.1-rc.17","status":"affected"}]}],"references":["https://github.com/h3js/h3/security/advisories/GHSA-2j6q-whv2-gh6w"],"weaknesses":["CWE-706"],"ingestedAt":"2026-10-29T20:11:40.391Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/33xxx/CVE-2026-33490.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-33490","state":"PUBLISHED","datePublished":"2026-03-26T17:19:15.956Z","dateUpdated":"2026-03-26T18:23:39.653Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-03-20T16:16:48.971Z"},"containers":{"cna":{"title":"h3: Missing Path Segment Boundary Check in `mount()` Causes Middleware Execution on Unrelated Prefix-Matching Routes","descriptions":[{"lang":"en","value":"H3 is a minimal H(TTP) framework. In versions 2.0.0-0 through 2.0.1-rc.16, the `mount()` method in h3 uses a simple `startsWith()` check to determine whether incoming requests fall under a mounted sub-application's path prefix. Because this check does not verify a path segment boundary (i.e., that the next character after the base is `/` or end-of-string), middleware registered on a mount like `/admin` will also execute for unrelated routes such as `/admin-public`, `/administrator`, or `/adminstuff`. This allows an attacker to trigger context-setting middleware on paths it was never intended to cover, potentially polluting request context with unintended privilege flags. Version 2.0.2-rc.17 contains a patch."}],"affected":[{"vendor":"h3js","product":"h3","versions":[{"version":">= 2.0.1-alpha.0, < 2.0.1-rc.17","status":"affected"}]}],"references":[{"url":"https://github.com/h3js/h3/security/advisories/GHSA-2j6q-whv2-gh6w","name":"https://github.com/h3js/h3/security/advisories/GHSA-2j6q-whv2-gh6w","tags":["x_refsource_CONFIRM"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"HIGH","attackVector":"NETWORK","availabilityImpact":"NONE","baseScore":3.7,"baseSeverity":"LOW","confidentialityImpact":"NONE","integrityImpact":"LOW","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-706","lang":"en","description":"CWE-706: Use of Incorrectly-Resolved Name or Reference","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-03-26T17:19:15.956Z"},"source":{"advisory":"GHSA-2j6q-whv2-gh6w","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","references":[{"url":"https://github.com/h3js/h3/security/advisories/GHSA-2j6q-whv2-gh6w","tags":["exploit"]}],"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-03-26T17:46:14.997707Z","id":"CVE-2026-33490","options":[{"Exploitation":"poc"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-03-26T18:23:39.653Z"}}]}}}